NEW YORK — David Lyle, CEO of the National Geographic Channel, has seen enough of the letters to know how they go. The writer is typically a longtime reader of the magazine, who perhaps recalls the times he leafed through its glossy pages while perched on grandpa’s knee.

“The second paragraph,” he said, “would always be, `So you can imagine my disappointment when ...”’

Fill in the blank. Maybe the person saw the channel’s documentary about escort services, or a show about a man who sculpts with a chain saw. Perhaps it was a show about gypsies, UFO hunters or people stocking up for the imminent end of the world. Maybe more letters will come after this Sunday, when narrator Rob Lowe starts a nostalgic three-day look at the 1980s.

Every day Lyle and his executive team face the challenge of building a successful network in the era of Honey Boo Boo and “Duck Dynasty” without damaging a National Geographic brand that has stood for quality since the magazine was first published in 1888.

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The first three months of 2013 represented the network’s best quarter since its launch in 2001. The National Geographic Channel averaged 554,000 viewers in prime time, propelled by “Doomsday Preppers,” the “Wicked Tuna” series about fishermen in Gloucester, Mass., and a movie dramatization of Bill O’Reilly’s book, “Killing Lincoln.”

“We have a lot to grow on,” Lyle said. “We have just scratched the surface with the types of shows and the types of people and ideas we can explore.”

Toward the end of 2011, Lyle appointed Howard Owens, a founder of Reveille Productions, as the network’s president and brought on Courteney Monroe from HBO as chief marketer. The station is a joint venture between National Geographic and the Fox cable networks.

Before its makeover, NatGeo was a musty network that aired documentaries with “voice of God” narrators and few reasons for people to watch regularly, Lyle said. The “Great Migrations” miniseries about animal treks in 2010 had spectacular nature photography but wasn’t the television event that executives hoped for.

“Just because we’re able to say `five years in the making’ doesn’t mean the audience gives a toss,” he said.

The new team’s mandate was to make the channel contemporary and “add the big E — entertainment” without alienating people, he said.

Financial success for many cable networks now requires developing characters and series that compel viewer loyalty. The History channel was once the place for old men to watch war movies. Now it’s the home of “Pawn Stars,” “American Pickers” and the just-concluded miniseries on the Bible. Its turnaround provided a blueprint for some of the Discovery networks and A&E, and now National Geographic.

Owens, whose former production company was behind shows like “The Biggest Loser” and “Master Chef,” was told to take some swings quickly. Not all connected, like last year’s “Chasing UFOs,” about alien hunters, or “American Gypsies.”

The experience taught a few lessons, particularly with the series “American Gypsies.” Viewers in focus groups told National Geographic the characters were obnoxious and their situations felt cheesy and manufactured.

“People turn to National Geographic to be captivated, to be taken away and maybe to learn something,” Owens said. “This was brash entertainment for entertainment’s sake, and that didn’t work for us.”

That knowledge enabled executives to hone in on where the traditional National Geographic brand and a new National Geographic Channel could intersect. They feel people look to National Geographic for access to something they wouldn’t normally see, often someplace compelling visually.

One of the reasons that “Wicked Tuna” works — aside from its great title — is that the characters are doing what they normally do, “and our cameras happen to be there catching it,” Owens said. Another popular series is “Inside Combat Rescue,” which follows military rescue units in Afghanistan.

While odd subcultures are often the focus of series, Owens said the network is looking to celebrate them, not make fun of them. That is not how a Montana religious sect felt after they let cameras in to film “American Colony: Meet the Hutterites,” which aired last year. They complained the series mocked and degraded them. National Geographic defended the series, and may be wading into similar choppy waters next month with the debut of “Polygamy Town,” about an Arizona community with men who have multiple wives.

There clearly have been culture clashes between supporters of the National Geographic Society, the scientific and educational institution that publishes the magazine and partly owns the channel, and the National Geographic Channel.

“The channel has become to National Geographic what the Frankenstein monster became to Dr. Frankenstein,” said Alan Mairson, a former writer and editor at the National Geographic magazine. He writes a blog, societymatters.org, that claims the channel hurts the society’s reputation but is tolerated because of the money it brings in. Several people have told him they gave up their society membership because of something on the channel.

One image unlikely to be seen in society educational material: a picture of a woman holding a leash attached to a dog collar around the neck of another woman, which promotes the network’s series “Taboo.” It’s described as being about behaviors accepted in some cultures but not in others.

The society’s outgoing CEO, John Fahey, said some of the channel’s past programming choices didn’t help the brand, primarily because there was an attempt to emulate what other networks were doing.

“The channel has clearly decided that they wanted to make sure the shows are smarter shows and reflect the brand,” Fahey said. “We’re not quite there yet but we are making good progress.”

Protecting the brand is important, but so is attracting viewers. Programmers can’t look down their noses at people, he said.

Fahey praised the upcoming “Brain Games,” which premieres April 22 and puts the brain through a series of experiments and optical illusions. The returning series “Locked up Abroad” on April 17 tells the story of former Vietnam War soldier Ernie Brace, a friend of John McCain who was held captive for nearly eight years.

Two series in May go north as the weather heats up. “Life Below Zero” heads to one of non-fiction TV’s favorite locations, Alaska, to explore the lives of people who live on their own in remote corners of the state. “Ultimate Survival Alaska” follows a group of outdoorsmen put to the test.

In an effort to find its own indelible characters, the channel will premiere “The Legend of Mick Dodge” in the fall. It follows a man who lives in the wilderness outside of Seattle, described by Owens as “Forrest Gump meets Middle-earth.”

The network’s approach is to be risk takers. Owens said that’s been a part of the National Geographic DNA for over a hundred years.